Which of the following will undergo sulphonation at fastest rate?

Product is:

${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{Br} \stackrel{\mathrm{AgCN}}{\to } \mathrm{A} \stackrel{{\mathrm{H}}_3{\mathrm{O}}^{+}}{⟶} \mathrm{HCOOH}+\mathrm{B}$;

$\mathrm{B} \underset{\mathrm{KOH}}{\overset{{\mathrm{CHCl}}_3}{\to }} \mathrm{A} \stackrel{\mathrm{Reduction} }{\to } \mathrm{C}$

$\mathrm{A},\mathrm{B},\mathrm{C}$ respectively in the above sequence are:

The product formed in the reaction is

is